Gastrin receptor-avid peptide conjugates

ABSTRACT

A compound for use as a therapeutic or diagnostic radiopharmaceutical includes a group capable of complexing a medically useful metal attached to a moiety which is capable of binding to a gastrin releasing peptide receptor. A method for treating a subject having a neoplastic disease includes administering to the subject an effective amount of a radiopharmaceutical having a metal chelated with a chelating group attached to a moiety capable of binding to a gastrin releasing peptide receptor expressed on tumor cells with subsequent internalization inside of the cell. A method of forming a therapeutic or diagnostic compound includes reacting a metal synthon with a chelating group covalently linked with a moiety capable of binding a gastrin releasing peptide receptor.

This application is based on Provisional Application which was filed onApr. 22, 1997, Ser. No. 60/044,049.

GRANT REFERENCE

The research carried out in connection with this invention was supportedin part by a grant from the Department of Energy (DOE), grant numberDE-FG02-89ER60875, a grant from the U.S. Department of Veterans AffairsMedical Research Division and the Department of Radiology MU-C2-02691.The Government has certain rights in the invention.

TECHNICAL FIELD

This invention relates to radionuclide-labeled compounds useful asradiopharmaceuticals. More particularly, the present invention relatesto conjugates of bombesin (BBN) analogues and a metal complexing groupwhich, when complexed to a radionuclide, are useful therapeutic andimaging agents for cancer cells that express gastrin releasing peptide(GRP) receptors.

BACKGROUND OF THE INVENTION

Detection and treatment of cancers using radiopharmaceuticals thatselectively target cancers in human patients has been employed forseveral decades. Unfortunately, only a limited number of site-directedradiopharmaceuticals that exhibit highly specific in vivo localizationin or near cancer cells are currently in routine use, as being approvedby the United States Food and Drug Administration (FDA). There is agreat deal of interest in developing new radioactive drugs due to theemergence of more sophisticated biomolecular carriers that have highaffinity and high specificity for in vivo targeting of tumors. Severaltypes of agents are being developed and have been investigated includingmonoclonal antibodies (MAbs), antibody fragments (F_(AB)'s and(F_(AB))₂'s), receptor-avid peptides [Bushbaum, 1995; Fischman et al.,1993; Schubiger et al. 1996].

The potential utility of using radiolabeled receptor-avid peptides forproducing radiopharmaceuticals is best exemplified by¹¹¹In-DTPA-conjugated octreotide (an FDA approved diagnostic imagingagent, Octreoscan®, marketed in the United States by MallinckrodtMedical, Inc.) [Lowbertz et al. 1994]. This radiopharmaceutical is an¹¹¹In-DTPA conjugate of Octreotide, a small peptide analogue of thehuman hormone somatostatin. This drug specifically binds to somatostatinreceptors that are over-expressed on neuroendocrine cancers (e.g.,carcinoid Ca, neuroblastoma, etc.) as well as others [Kenning et al.,1994]. Since indium-111 (¹¹¹In) is not the ideal radionuclide forscintigraphic imaging, other somatostatin analogues and otherreceptor-avid biomolecules that are labeled with ^(99m)Tc (the optimalradionuclide for diagnostic imaging) are being studied and developed[Eckelman, 1995; Vallabhajosula et al., 1996].

Bombesin (BBN) is a 14 amino acid peptide that is an analogue of humangastrin releasing peptide (GRP) that binds to GRP receptors with highspecificity and has an affinity similar to GRP [Davis et al., 1992]. GRPreceptors have been shown to be over-expressed or uniquely expressed onseveral types of cancer cells. Binding of GRP receptor agonists (alsoautocrine factors) increases the rate of cell division of these cancercells. For this reason, a great deal of work has been, and is beingpursued to develop BBN or GRP analogues that are antagonists [Davis etal., 1992; Hoffken, 1994; Moody et al., 1996; Coy et al., 1988; Cai etal., 1994]. These antagonists are designed to competitively inhibitendogenous GRP binding to GRP receptors and reduce the rate of cancercell proliferation [Hoffken, 1994]. Treatment of cancers using theseantagonists with these non-radioactive peptides requires chronicinjection regimens (e.g., daily, using large quantities of the drug).

In designing an effective receptor-avid radiopharmaceutical for use as adiagnostic or therapeutic agent for cancer, it is important that thedrug have appropriate in vivo targeting and pharmacokinetic properties[Fritzberg et al., 1992; Eckelman et al., 1993]. For example, it isessential that the radiolabeled receptor-avid peptide have high specificuptake by the cancer cells (e.g., via GRP receptors). In addition, it isnecessary that once the radionuclide localizes at a tumor site, it mustremain there for an extended time to deliver a highly localizedradiation dose to the tumor. In order to achieve sufficiently highspecific uptake of radiolabeled BBN analogues in tumors, the bindingaffinity of promising derivatives must be high (i.e., K_(d)1≈1-5 nmolaror less) with prolonged retention of radioactivity [Eckelman et al.,1995; Eckelman, et al., 1993]. Work with ¹²⁵I-BBN derivatives has shown,however, that for cancer cells that bind the ¹²⁵I-BBN derivatives(whether they be agonists or antagonists), the radioactivity is eitherwashed off or expelled from the cells (in vitro) at a rapid rate[Hoffman et al., 1997]. Thus, these types of derivatives have a lowprobability of remaining “trapped” at the tumor site (in vivo)sufficiently long to be effective therapeutic or diagnostic agents.

Developing radiolabeled peptides that are cleared efficiently fromnormal tissues is also an important and especially critical factor fortherapeutic agents. When labeling biomolecules (e.g., MAb, F_(AB)'s orpeptides) with metallic radionuclides (via a chelate conjugation), alarge percentage of the metallic radionuclide (in some chemical form)usually becomes “trapped” in either the kidney or liver parenchyma(i.e., is not excreted into the urine or bile) [Duncan et al., 1997;Mattes, 1995]. For the smaller radiolabeled biomolecules (i.e., peptidesor F_(AB)'s), the major route of clearance of activity is through thekidneys which in turn retain high levels of the radioactive metal (i.e.,normally>10-15% of the injected dose) [Duncan et al., 1997]. Tispresents a major problem that must be overcome in the development oftherapeutic agents that incorporate metallic radionuclides, otherwisethe radiation dose to the kidneys would be excessive. For example,¹¹¹In-octreotide, the FDA approved diagnostic agent, exhibits highuptake and retention in kidneys of patients [Eckelman et al., 1995].Even though the radiation dose to the kidneys is higher than desirable,it is tolerable in that it is a diagnostic radiopharmaceutical (it doesnot emit alpha- or beta-particles), and the renal dose does not produceobservable radiation induced damage to the organ.

It has now been found that conjugating BBN derivatives which areagonists in non-metallated conjugates which that exhibit bindingaffinities to GRP receptors that are either similar to or approximatelyan order of magnitude lower than the parent BBN derivative. [Li et al.,1996a]. These data coupled with our recent results show that it is nowpossible to add radiometal chelates to BBN analogues, which areagonists, and retain GRP receptor binding affinities that aresufficiently high (i.e., approx. 1-5 nmolar K_(d)'s) for furtherdevelopment as potential radiopharmaceuticals. These agonist conjugatesare transported intracellularly after binding to cell surface GRPreceptors and retained inside of the cells for extended time periods. Inaddition, in vivo studies in normal mice have shown that retention ofthe radioactive metal in the kidneys was low (i.e., <5%) with themajority of the radioactivity excreted into the urine.

According to one aspect of the present invention, there is provided aBBN conjugate consisting of essentially a radio-metal chelate covalentlyappended to the receptor binding region of BBN [e.g., BBN(8-14)] to formradiolabeled BBN analogues that have high specific binding affinitieswith GRP receptors. These analogues are retained for long times insideof GRP expressing cancer cells. Furthermore, their clearance from thebloodstream, into the urine with minimal kidney retention, is efficient.Preferably, the radiometals are selected from ^(99m)Tc, ^(186/188)Re,¹⁰⁵Rh, ¹⁵³Sm, ¹⁶⁶Ho, ⁹⁰Y or ¹⁹⁹Au, all of which hold the potential fordiagnostic (i.e., ^(99m)Tc) or therapeutic (i.e., ^(186/188)Re, ¹⁰⁵Rh,¹⁵³Sm, ¹¹⁶Ho, ⁹⁰Y, and ¹⁹⁹Au) utility in cancer patients [Schubiger etal, 1996; Eckelman, 1995; Troutner, 1978].

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a compoundfor use as a therapeutic or diagnostic radiopharmaceutical whichincludes a group which is capable of complexing a metal attached to amoiety capable of binding to a gastrin releasing peptide receptor.

Additionally, in accordance with the present invention, a method fortreating a subject having a neoplastic disease which includes the stepof administering to the subject an effective amount of aradiopharmaceutical having a metal chelated with a chelating groupattached to a moiety capable of binding to a gastrin releasing peptidereceptor on a cancer cell, subsequently intracellularly transported andresidualized inside the cell, is disclosed.

Additionally, in accordance with the present invention, a method offorming a therapeutic or diagnostic compound including the step ofreacting a metal synthon with a chelating group covalently linked with amoiety capable of binding a gastrin releasing peptide receptor isdisclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated asthe same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 illustrates a radiometal conjugate according to the presentinvention;

FIG. 2 is an ORTEP drawing of the {Rh[16]aneS₄-olCl₂}⁺, illustrating thecrystal structure a Rhodium macrocycle;

FIG. 3 illustrates a coupling reaction wherein a spacer group is coupledto a bombesin agonist binding moiety;

FIG. 4 illustrates a coupling reaction for coupling a metal chelate to apeptide;

FIG. 5 illustrates several iodinated bombesin analogues including theirIC₅₀'s;

FIG. 6 illustrates several tethered bombesin analogues;

FIG. 7 illustrates several [16]aneS₄ bombesin analogues;

FIG. 8 is a graph illustrating IC₅₀ analysis wherein %-I-125-BBN totaluptake versus molar concentration of displacing ligand is shown;

FIG. 9 illustrates several Rhodium-[16]aneS₄ bombesin analogues;

FIG. 10 illustrates an HTLC chromatogram of Rhodiumn-BBN-37 wherein (A)illustrates ¹⁰⁵RhCl₂-BBN-37 and (B) illustrates RhCl₂-BBN-37;

FIG. 11 is a graph illustrating ¹²⁵I-Tyr⁴-bombesin internalizationefflux from Swiss 3T3 cells;

FIG. 12 illustrates 1-125 bombesin internalization efflux in I-125 freebuffer wherein ¹²⁵I-Tyr⁴-BBN vs. ¹²⁵I-Lys³-BBN efflux from Swiss 3T3cells is shown;

FIG. 13 is a graph illustrating the efflux of ¹⁰⁵Rh-BBN-37 from Swiss3T3 cells;

FIG. 14 illustrates several ¹⁰⁵Rhodium bombesin analogues includingtheir IC₅₀'s;,

FIG. 15 is a graph illustrating ¹⁰⁵Rh-BBN-61 efflux from Swiss 3T3cells;

FIG. 16 is a graph illustrating the efflux of ¹⁰⁵Rh-BBN-22 vs.¹⁰⁵Rh-BBN-37 from Swiss 3T3 cells;

FIG. 17 are graphs illustrating Pancreatic CA cell binding wherein (A)illustrates the efflux ¹²⁵I-Tyr⁴-BBN from CF PAC1 cells and (B)illustrates the efflux of ¹⁰⁵Rh-BBN-37 from CF PAC1 cells; and

FIG. 18 are graphs illustrating Prostate CA cell binding wherein (A)illustrates the efflux of 125-Tyr⁴-BBN from PC-3 cells and (B)illustrates the efflux of ¹⁰⁵Rh-BBN-37 from PC-3 cells.

FIG. 19 illustrates 5 [16]aneS₄ bombesin analogues.

FIG. 20 illustrates 4 Rhodium-[16]aneS₄ bombesin analogues.

FIG. 21 illustrates 3 different N₃S-BFCA conjugates of BBN(7-14).

FIG. 22 illustrates on HPLC chromatogram of ^(99m)Tc-BBN-122.

FIG. 23 is a graph illustrating ^(99m)TC-BBN-122 internalization effluxfrom human prostate cancer cells (PC-3 cells).

FIG. 24 is a graph illustrating ^(99m)Tc-BBN-122 internalization effluxfrom human pancreatic tumor cells (CFPAC-1 cells).

FIG. 25 is a graph illustrating ^(99m)Tc-RP414-BBN42 retention in PC-3prostate cancer cells.

FIG. 26 is a graph illustrating 99mTc42 retention in CFPAC-1 pancreaticcancer cells.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, compounds for use as diagnosticand/or therapeutic radiopharmaceuticals include a group capable ofcomplexing a metal attached to a moiety capable of binding to a gastrinreleasing peptide (GRP) receptor as shown in FIG. 1. The moiety capableof specific binding to the GRP receptor is a GRP agonist. A GRP agonistwould activate or produce response by the GRP receptor upon interactionwith the GRP receptor and would be subsequently internalized inside ofthe cell by endocytosis. In contrast, a GRP antagonist would counteractthe effect of an agonist and would not be internalized inside of thecell.

More specifically, the GRP agonist is a compound such as selected aminoacid sequences or peptidomimetics which are known to activate the cellfollowing binding with high affinity and selectivity to GRP receptorsand that can be covalently linked to the metal complexing group. Manyexamples of specific modifications of the BBN(8-14) that can be made toproduce sequences with high antagonistic and agonistic binding affinityfor GRP repectors have been reported by numerous investigations [Daviset al., 1992; Hoffken, 1994; Moody et al., 1996; Coy et al., 1988; Caiet al., 1994; Moody et al., 1995; Leban et al., 1994; Cai et al., 1992].

In a preferred embodiment of the present invention, the metal complexinggroup or moiety is a chelating agent or chelator which complexes tometals such as ¹⁰⁵Rh—, ^(186/188)Re—, ^(99m)Tc, ¹⁵³Sm, ¹⁶⁶Ho, ⁹⁰Y or¹⁹⁹Au. The chelating agent or chelator is attached or bound to the GRPagonist “binding region” to produce a conjugate that retains itscapability for high affinity and specific binding to GRP receptors.

In a more preferred embodiment of the present invention, the GRP agonistis a bombesin (BBN) analogue and/or a derivative thereof. The BBNderivative or analog thereof preferably contains either the same primarystructure of the BBN binding region [i.e., BBN(8-14)] or similar primarystructures, with specific amino acid substitutions, that willspecifically bind to GRP receptors with better or similar bindingaffinities as BBN alone (i.e., K_(d)≈1-5 nmolar) Compounds containingthis BBN binding region (or binding moiety), when covalently linked toother groups (e.g., a radiometal chelate), are also referred to as BBNconjugates.

In general, the compounds of the present invention have a structure ofthe general formula:X-Y-Bwherein X is a group capable of complexing a metal, such as aradiometal; Y is a covalent bond on a spacer group; and B is a bombesinagonist binding moiety.

The metal bound to the metal complexing group can be any suitable metalchosen for a specific therapeutic or diagnostic use including transitionmetals and y and x emitting isotopes. Preferably, the metal is aradiometal such as ¹⁰⁵Rh-, ^(99m)Tc-, ^(186/188)Re, ¹⁵³Sm-, ¹⁶⁶Ho-,⁹⁰Y-, and ¹⁹⁹Au- whose chelates can be covalently linked (i.e.,conjugated) to the specific BBN binding region via the N-terminal end ofthe primary binding sequence (e.g., BBN-8 or Trp⁸) as shown in FIG. 1.

In a preferred embodiment, the radiometal complexes are positioned bybeing spaced apart from or remotely from the amino acid Trp⁸ by thespacer groups. The spacer groups can include a peptide (i.e., ≧1 aminoacid in length), a hydrocarbon spacer of C₁-C₁₀ or a combination ofthereof. Preferably, the hydrocarbon spacer has is a C₃-C₉ group. Theresulting radio-labeled BBN conjugates retain high binding affinity andspecificity for GRP receptors and are subsequently internalized insideof the cell.

The BBN conjugates can further incorporate a spacer group or componentto couple the binding moiety to the metal chelator (or metal bindingbackbone) while not adversely affecting either the targeting function ofthe BBN-binding moiety or the metal complexing function of the metalchelating agent.

The term “spacer group” or “linker” refers to a chemical group thatserves to couple the BBN binding moiety to the metal chelator while notadversely affecting either the targeting function of the BBN bindingmoiety or the metal complexing function of the metal chelator. Suitablespacer groups include peptides (i.e., amino acids linked together)alone, a non-peptide group (e.g., hydrocarbon chain) or a combination ofan amino acid sequence and a non-peptide spacer. The type of spacergroup used in most of the experimental studies described below in theExamples section were composed of a combination of L-glutamine andhydrocarbon spacers. A pure peptide spacer could consist of a series ofamino acids (e.g., diglycine, triglycine, gly-gly-glu, etc.), in whichthe total number of atoms between the N-terminal residue of the BBNbinding moiety and the metal chelator in the polymeric chain is ≦12atoms.

The spacer can also include a hydrocarbon chain [i.e., R₁—(CH₂)_(n)—R₂]wherein n is 0-10, preferably n=3 to 9, R₁ is a group (e.g., H₂N—, HS—,—COOH) that can be used as a site for covalently linking the ligandbackbone or the performed metal chelator or metal complexing backbone;and R₂ is a group that is used for covalent coupling to the N-terminalNH₂-group of the BBN binding moiety (e.g., R₂ is an activated COOHgroup). Several chemical methods for conjugating ligands (i.e.,chelators) or preferred metal chelates to biomolecules have been welldescribed in the literature [Wilbur, 1992; Parker, 1990; Hermanson,1996; Frizberg et al., 1995]. One or more of these methods could be usedto link either the uncomplexed ligand (chelator) or the radiometalchelate to the spacer group or to link the spacer group to the BBN(8-14)derivatives. These methods include the formation of acid anhydrides,aldehydes, arylisothiocyanates, activated esters, orN-hydroxysuccinmides [Wilbur, 1992; Parker, 1990; Hermanson, 1996;Frizberg et al., 1995].

The term “metal complexing chelator” refers to a molecule that forms acomplex with a metal atom that is stable under physiological conditions.That is, the metal will remain complexed to the chelator backbone invivo. More particularly, a metal complexing chelator is a molecule thatcomplexes to a radionuclide metal to form a metal complex that is stableunder physiological conditions and which also has at least one reactivefunctional group for conjugation with the BBN agonist binding moiety.Metal complexing chelators can include monodentate and polydentatechelators [Parker, 1990; Frizberg et al., 1995; Lister-James et. al.,1997; Li et al., 1996b; Albert et al., 1991; Pollak et al., 1996; deJong et al., 1997; Smith et al., 1997]. Metal complexing chelatorsinclude tetradentate metal chelators which can be macrocyclic and have acombination of four nitrogen and/or sulphur metal-coordinating atoms[Parker et al., 1990; Li et al., 1996b] and are designated as N₄, S₄,N₃S, N₂S₂, NS₃, etc. as shown in FIG. 2. A number of suitablemultidentate chelators that have been used to conjugate proteins andreceptor-avid molecules have been reported [Frizberg, et al., 1995;Lister-James et al., 1997; Li et al., 1996b; Albert et al., 1991; Pollaket al., 1996; de Jong et al., 1997]. These multidentate chelators canalso incorporate other metal-coordinating atoms such as oxygen andphosphorous in various combinations. The metal binding complexing moietycan also include “3+1” chelators [Seifert et al., 1998].

For diagnostic purposes, metal complexing chelators preferably includechelator backbones for complexing the radionuclide metal ^(99m)Tc. Fortherapeutic purposes, metal complexing chelators preferably includechelator backbones that complex the radionuclide metals ¹⁰⁵Rh,^(186/188)Re, ¹⁵³Sm, ⁹⁰Y, ¹⁶⁶Ho, and ¹⁹⁹Au [Schubiger et al.,1996;Hoffken, 1994].

As was briefly described above, the term “bombesin agonist” or “BBNagonist” refers to compounds that bind with high specificity andaffinity to GRP receptors, and upon binding to the GRP receptor, areintracellularly internalized. Suitable compounds include peptides,peptidomimetics and analogues and derivatives thereof. In particular,previous work has demonstrated that the region on the BBN peptidestructure required for binding to GRP receptors spans from residue 8through 14 [Davis et al., 1992; Hoffken, 1994; Moody et al., 1996; Coy,1988; Cai et al., 1994]. The presence of metnionine (Met) at positionBBN-14 will generally confer agonistic properties while the absence ofthis residue at BBN-14 generally confers antagonistic properties[Hoffken, 1994].

It is well documented in the art that there are a few and selectivenumber of specific ammo acid substitutions in the BBN (8-14) bindingregion (e.g., D-Ala¹¹ for L-Gly¹¹ or D-Trp⁸ for L-Trp⁸), which can bemade without decreasing binding affinity [Leban et al., 1994; Qin etal., 1994; Jensen et al., 1993]. In addition, attachment of some aminoacid chains or other groups to the N-terminal amine group at positionBBN-8 (i.e., the Trp⁸ residue) can dramatically decrease the bindingaffinity of BBN analogues to GRP receptors [Davis et al., 1992; Hoffken,1994; Moody et al., 1996; Coy, et al., 1988; Cai et al., 1994]. In a fewcases, it is possible to append additional amino acids or chemicalmoieties without decreasing binding affinity. The effects of conjugatingvarious side chains to BBN-8 on binding affinity, therefore, is notpredicable.

The BBN conjugates of the present invention can be prepared by variousmethods depending upon the selected chelator. The peptide portion of theconjugate can be most conveniently prepared by techniques generallyestablished and known in the art of peptide synthesis, such as thesolid-phase peptide synthesis (SPPS) approach. Solid-phase peptidesynthesis (SPPS) involves the stepwise addition of amino acid residuesto a growing peptide chain that is linked to an insoluble support ormatrix, such as polystyrene. The C-terminal residue of the peptide isfirst anchored to a commercially available support with its amino groupprotected with an N-protecting agent such as a t-butyloxycarbonyl group(tBoc) or a fluorenylmethoxycarbonyl (FMOC) group. The amino protectinggroup is removed with suitable deprotecting agents such as TFA in thecase of TBOC or piperidine for FMOC and the next amino acid residue (inN-protected form) is added with a coupling agent such asdicyclocarbodjimide (DCC). Upon formation of a peptide bond, thereagents are washed from the support. After addition of the finalresidue, the peptide is cleaved from the support with a suitable reagentsuch as trifluoroacetic acid (TFA) or hydrogen fluoride (HF).

The spacer groups and chelator components are then coupled to form aconjugate by reacting the free amino group of the Trp³ residue of theBBN binding moiety with an appropriate functional group of the chelator,metal chelator or spacer group, such as a carboxyl group or activatedester.

The BBN conjugate can also incorporate a metal complexing chelatorbackbone that is peptidic and compatible with solid-phase peptidesynthesis. In this case, the chelator backbone can be added to the BBNbinding moiety in the same manner as described above or, moreconveniently, the metal completing chelator backbone coupled to the BBNbinding moiety can be synthesized in toto starting from the C-terminalresidue of the peptide and ending with the N-terminal residue of themetal complexing chelator structure.

The chelator backbones used in accordance with the present invention arecommercially available or they could be made by methods similar to thoseoutlined in the literature [Frizberg et al., 1995; Lister-James et al.,1997; Li et al., 1996b; Albert et al., 1991; Pollak et al., 1996; deJong et al., 1997; Smith et al., 1997; Seifert et al., 1998]. Attachmentof the spacer groups to functionalizable atoms appended to the ligandbackbone can be performed by standard methods known to those skilled inthe art. For example, the HOBt/HBTU activated —COOH group on5-aminovaleric acid (5-AVA) was reacted with the N-terminal amine onGln⁷ to produce an amide linkage as shown in FIG. 3. Similarly, the—COOH group attached to the characterized [16]aneS₄ ligand wasconjugated to the amine group on the hydrocarbon spacer (shown below) byreaction of the HOBt/HBTU activated carboxyl group appended to the[16]aneS₄ macrocycle with the terminal amine group on 5-AVA to formBBN-37 as shown in FIG. 4. Other standard conjugation reactors thatproduce covalent linkages with amine groups can also be used [Wilbur,1992; Parker, 1990].

The chelating framework, conjugated via Trp⁸, complexes the radiometalsshould form a 1:1 chelator to metal ratio. Since ^(99m)Tc has a shorthalf-life (6 hour) and is a diagnostic radionuclide, the method offorming the ^(99m)Tc-BBN analogues should permit complexation (eitherdirectly or by transmetallation) of ^(99m)Tc to the conjugated chelatingframework in a one-step, high yield reaction (exemplified below in theExperimental Section).

In contrast, the longer half lives of the therapeutic radionuclides(e.g., ¹⁰⁵Rh, ^(186/188)Re, ¹⁵³Sm, ¹⁶⁶Ho, ⁹⁰Y, or ¹⁹⁹Au) permitformation of the corresponding radiolabeled BBN analogues by either aone step high yield complexation step or by performing a ¹⁰⁵Rh—,^(186/188)Re—, ¹⁵³Sm, ¹⁶⁶Ho, ⁹⁰Y or ¹⁹⁹Au chelate synthon followed byconjugation of the performed complex to the. N-terminal end of the BBNbinding moiety. In all cases, the resulting specific activity of thefinal radiolabeled BBN derivative must be high (i.e., >1 Ci/μmole).

Re- and Tc-conjugates

Re and Tc are both in row VIIB of the Periodic Table and they arechemical congeners. Thus, for the most part, the complexation chemistryof these two metals with ligand frameworks that exhibit high in vitroand in vivo stabilities are the same [Eckelman, 1995]. Many ^(99m)Tc or^(186/188)Re complexes, which are employed to form stable radiometalcomplexes with peptides and proteins, chelate these metals in their +5oxidation state [Lister-James et al., 1997]. This oxidation state makesit possible to selectively place ^(99m)Tc— or ^(186/188)Re into ligandframeworks already conjugated to the biomolecule, constructed from avariety of ^(99m)Tc(V) and/or ^(186/188)Re(V) weak chelates (e.g.,^(99m)Tc—glucoheptonate, citrate, gluconate, etc.) [Eckelman, 1995;Lister-Jarnes et al., 1997; Pollak et al., 1996]. Tetradentate ligandframeworks have been shown to form well-defined, single chemical speciesin high specific activities when at least one thiol group or at leastone hydroxymethylene phosphine group is present on the ligand backbone[Smith et al., 1997].

Ligands which form stable Tc(V) or Re(V) tetradentate complexescontaining, but not limited to, amino N-atoms, amido-N-atoms,carboxy-O-atoms and thioether-S-atoms, are donor atoms that can also bepresent [Eckelman, 1995; Fritzberg et al., 1992; Parker, 1990; Frizberget al., 1995; Pollak et al., 1996; Seifert et al., 1998]. Depending uponthe mix of donor atoms (groups), the overall complex charge normallyranges from −1 to +1.

Incorporation of the metal within the conjugate can be achieved byvarious methods commonly known in the art of coordination chemistry.When the metal is technetium—99m, the following general procedure can beused to form a technetium complex. A peptide-chelator conjugate solutionis formed by initially dissolving the conjugate in aqueous alcohol suchas ethanol. The solution is then degassed to remove oxygen. When an —SHgroup is present in the peptide, the thiol protecting group are removedwith a suitable reagent, for example with sodium hydroxide, and are thenneutralized with an organic acid such as acetic acid (pH 6.0-6.5). Inthe labeling step, sodium pertechnetate obtained from a molybdenumgenerator is added to a solution of the conjugate with a sufficientamount of a reducing agent, such as stannous chloride, to reducetechnetium and is then heated. The labeled conjugate can be separatedfrom the contaminants ^(99m)TcO₄ ⁻ and colloidal ^(99m)TcO₂chromatographically, for example with a C-18 Sep Pak cartridge [MlliporeCorporation, Waters Chromatography Division, 34 Maple Street, Milford,Mass. 01757].

In an alternative method, the labeling can be accomplished by atranschelation reaction. The technetium source is a solution oftechnetium complexed with labile ligands facilitating ligand exchangewith the selected chelator. Examples of suitable ligands fortranschelation includes tartrate, citrate, gluconate, andheptagluconate. It will be appreciated that the conjugate can be labeledusing the techniques described above, or alternatively, the chelatoritself may be labeled and subsequently coupled to the peptide to formthe conjugate; a process referred to as the “prelabeled chelate” method.

When labeled with diagnostically and/or therapeutically useful metals,peptide-chelator conjugates or pharmaceutically acceptable salts,esters, amides, and prodrugs of the present invention can be used totreat and/or detect cancers, including tumors, by procedures establishedin the art of radiodiagnostics and radiotherapeutics. [Bushbaum, 1995;Fischman et al., 1993; Schubiger et al., 1996; Lowbertz et al., 1994;Krenning et al., 1994]. A conjugate labeled with a radionuclide metal,such as technetium-99m, can be administered to a mammal, including humanpatients or subjects, by intravenous or intraperitoneal injection in apharmaceutically acceptable carrier and/or solution such as saltsolutions like isotonic saline. The amount of labeled conjugateappropriate for administration is dependent upon the distributionprofile of the chosen conjugate in the sense that a rapidly clearedconjugate may be administered in higher doses than one that clears lessrapidly. Unit doses acceptable for Tc-99m imaging radiophannaceuticalsinflammation are in the range of about 5-40 mCi for a 70 kg individual.In vivo distribution and localization can be tracked by standardscintigraphic techniques at an appropriate time subsequent toadministration; typically between thirty minutes and 180 minutesdepending upon the rate of accumulation at the target site with respectto the rate of clearance at non-target tissue.

The compounds of the present invention can be administered to a patientalone or as part of a composition that contains other components such asexcipients, diluents, and carriers, all of which are well-known in theart. The compounds can be administered to patients either intravenouslyor intraperitoneally.

There are numerous advantages associated with the present invention. Thecompounds made in accordance with the present invention forms a stable,well-defined ^(99m)Tc or ^(186/188)Re conjugate analogues of BBNagonists. Similar BBN against analogues can also be made by usingappropriate chelator frameworks for the respective radiometals, to formstable-well-defined products labeled with ¹⁵³Sm, ⁹⁰Y, ¹⁶⁶Ho, ¹⁰⁵Rh or¹⁹⁹Au. The radiolabeled BBN agonist conjugates selectively bind toneoplastic cells expressing GRP receptors become internalized and areretained in the tumor cells for extended time periods. Incorporating thespacer group between the metal chelator and the BBN agonist bindingmoiety maximizes the uptake and retention of the radioactive metalinside of the neoplasts or cancer cells. The radioactive material thatdoes not reach (i.e., does not bind) the cancer cells is preferentiallyexcreted efficiently into the urine with minimal radiometal retention inthe kidneys.

The following examples are presented to illustrate specific embodimentsand demonstrate the utility of the present invention.

Experimental Section

EXAMPLE I Synthesis and In Vitro Binding Assessment of Synthetic BBNAnalogues Employing Hydrocarbon Chain Spacers

A. Synthesis:

Many BBN analogues were synthesized by Solid Phase Peptide Synthesis(SPPS). Each peptide was prepared by SPPS using an Applied BiosystemsModel 432A peptide synthesizer. After cleavage of each BBN analogue fromthe resin using Trifluoracetic acid (TFA), the peptides were purified byC₁₈ reversed-phase HPLC using a Vydac HS54 column and CH₃CN/H₂Ocontaining 0.1% TFA as the mobile phase. After collection of thefraction containing the desired BBN peptide (approx. 80-90% yield inmost cases), the solvent was evaporated. The identity of each BBNpeptide was confirmed by FAB-mass spectrometry, Department ofChemistry—Washington University, St. Louis, Mo.

Various amino acid sequences (in some cases including different chemicalmoieties) were conjugated to the N-terminal end of the BBN bindingregion (i.e., to BBN-8 or Trp⁸). BBN analogue numbers 9, 15, 15i, 16,16i and 18 were synthesized as examples of N-terminal modified peptidesas shown in FIG. 5.

Various tethered N-terminal (via Trp⁸) BBN analogues were alsosynthesized by SPPS as exemplified by BBN-40, BBN-41, BBN-42, BBN-43,BBN-44, BBN45, and BBN-49 as shown in FIG. 6. In these particulartethered peptides, a Glu residue was attached to Trp⁸ followed byattachment of FMOC protected terminal amine groups separated from a—COOH group by 3-, 4-, 5-, 6-, 8- and 11-carbon chain (CH) spacers (FIG.6). These FmOC protected acids were added as the terminal step duringthe SPPS cycle. As described previously, each of the BBN analogues waspurified by reversed-phase HPLC and characterized by high resolutionMass Spectroscopy. Peptide 49 employed only glutamine as the spacergroup.

The [16]aneS₄ macrocyclic ligand was conjugated to selected tethered BBNanalogues shown in FIG. 6. The —OCH₂COOH group on the [16]aneS₄macrocycle derivative was activated via HOBt/HBTU so that it efficientlyformed an amide bond with the terminal NH₂ group on the spacer side arm(following deprotection). The corresponding [16]aneS₄ tethered BBNderivatives were produced and examples of 4 of these derivatives (i.e.,BBN-22, -37, -46 and -47) are shown in FIG. 7. As previously described,each [16]aneS₄ BBN derivative was purified by reversed phase HPLC andcharacterized by FAB Mass Spectroscopy.

B. In Vitro Binding Affinities

The binding affinities of the synthetic BBN derivatives were assessedfor GRP receptors on Swiss 3T3 cells and, in some cases, on a variety ofhuman cancer cell lines, that express GRP receptors. The IC₅₀'s of eachderivative was determined relative to (i.e., in competition with)¹²⁵I-Tyr⁴-BBN (the K_(d) for ¹²⁵I-Tyr⁴BBN for GRP receptors in Swiss 3T3cells is reported to be 1.6±0.4 nM) [Zueht et al., 1991]. The cellbinding assay methods used to measure the IC₅₀'s is standard and wasused by techniques previously reported [Jensen et al., 1993; Cai et al.,1994; Cai et al., 1992]. The methods-used for determining IC₅₀'s withall GRP receptor binding of GRP receptors on all cell lines was similar.The specific method used to measure IC₅₀'s on Swiss 3T3 cells is brieflydescribed as follows:

Swiss 3T3 mouse fibroblasts are grown to confluence in 48 wellmicrotiter plates. An incubation media was prepared consisting of HEPES(11.916 g/l), NaCl (7.598 g/l), KCl (0.574 g/l), MgCl₂ (1.106 g/l), EGTA(0.380 g/l), BSA (5.0 g/l), chymostatin (0.002 g/l), soybean trypsininhibitor (0.200 g/l), and bacitracin (0.050 g/l). The growth media wasremoved, the cells were washed twice with incubation media, andincubation media was returned to the cells. ¹²⁵I-Tyr⁴-BBN (0.01 μCi) wasadded to each well in the presence of increasing concentrations of theappropriate competitive peptide. Typical concentrations of displacingpeptide ranged from 10⁻¹² to 10⁻⁵ moles of displacing ligand per well.The cells were incubated at 37° C. for forty minutes in a 95%O₂/5%CO₂humidified environment. At forty minutes post initiation of theincubation, the medium was discarded, and the cells were washed twicewith cold incubation media. The cells were harvested from the wellsfollowing incubation in a trypsin/EDTA solution for five minutes at 37°C. Subsequently, the radioactivity, per well, was determined and themaximum % total uptake of the radiolabeled peptide was determined andnormalized to 100%.

C. Results of Binding Affinity Measurements

The IC₅₀ values measured for the BBN derivatives synthesized inaccordance with this invention showed that appending a peptide sidechain and other moieties via the N-terminal BBN-8 residue (i.e., Trp⁸)produced widely varying IC₅₀ values. For example, see IC₅₀ values shownfor BBN 11, 15i, 16i, and 18 in FIGS. 5 and 8. The observations areconsistent with previous reports showing highly variable IC₅₀ valueswhen derivatizing BBN(8-13) or BBN(8-14) with a predominantly shortchain of amino acid residues [Hoffken, 1994]. In contrast, when ahydrocarbon spacer of 3- to 11-carbons was appended between BBN(7-14)and the [16]aneS₄ macrocycle, the IC₅₀'s were found to be surprisinglyrelatively constant and in the 1-5 nM range (i.e., see IC₅₀ values forBBN-22, -37, -46 and 47 as shown in FIG. 7). These data suggest thatusing relatively simple spacer groups to extend ligands some distancefrom the BBN binding region [e.g., BBN(8-14)] can produce derivativesthat maintain binding affinities in the 1-5 nmolar range.

D. Cell Binding Studies

Results illustrated in FIG. 9 show that when the RhCl₂-[16]aneS₄ complexseparated from Trp⁸ by only a glutamine (Glu⁷), the IC₅₀ of thisconjugate (i.e., Rh-BBN-22) was 37.5 nM. However, when a five (5) carbonspacer or an eight (8) carbon spacer was present (i.e., Rh-BBN-37 andRh-BBN-47), the IC₅₀'s remained below 5 nM as shown in FIG. 9. Thesedata demonstrate that a straight chain spacer (along with glu⁷) to movethe +1 charged Rh—S₄-chelate away from the BBN binding region willresult in a metallated BBN analogue with sufficiently high bindingaffinities to GRP receptors for in vivo tumor targeting applications.

E. ¹⁰⁵Radiolabeled BBN Analogues

The ¹⁰⁵Rh conjugates of BBN-22, BBN-37, BBN-46 and BBN47 weresynthesized using a ¹⁰⁵Rh-chloride reagent from the Missouri UniversityResearch Reactor (MURR). This reagent was obtained as ¹⁰⁵Rh-chloride, ano-carrier-added (NCA) product, in 0.1-1M HCl. The pH of this reagentwas adjusted to 4-5 using 0.1-1.0 M NaOH dropwise and it was added toapproximately 0.1 mg of the [16]aneS₄-conjugated BBN derivatives in 0.9%aqueous NaCl and 10% ethanol. After the sample was heated at 80° C. forone hour, the ¹⁰⁵Rh-BBN analogues were purified using HPLC. In eachcase, a NCA or high specific activity product was obtained since thenon-metallated S₄-BBN conjugates eluted at a retention time well afterthe ¹⁰⁵Rh-BBN conjugates eluted. For example, the retention time of¹⁰⁵Rh-BBN-37 was 7.1 min while BBN-37 eluted at 10.5 min from aC-18-reversed phase column eluted with CH₃CN/H₂O containing 0.1% TFA asshown in FIG. 10A-B.

EXAMPLE II Retention of ¹⁰⁵Rh-BBN Analogues in Cancer Cells

Once the radiometal has been specifically “delivered” to cancer cells(e.g., employing the BBN binding moiety that specifically targets GRPreceptors on the cell surface), it is necessary that a large percentageof the “delivered” radioactive atoms remain associated with the cellsfor a period time of hours or longer to make an effectiveradiopharmaceutical for effectively treating cancer. One way to achievethis association is to internalize the radiolabeled BBN conjugateswithin the cancer cell after binding to cell surface GRP receptors.

In the past, all of the work with synthetic-BBN analogues for treatmentof cancers focused on synthesizing and evaluating antagonists [Davis etal., 1992; Hoffken, 1994; Moody et al., 1996; Coy et al., 1988; Cai etal., 1994; Moody et al., 1995; Leban et al., 1994; Cai et al., 1992].After evaluating synthetic BBN analogues that would be predicted to beeither agonists or antagonists, applicants found that derivatives ofBBN(8-14) (i.e., those with the methioaine or amidated methionine atBBN-14) are rapidly internalized (i.e., in less than two minutes) afterbinding to the cell surface GRP receptors. Several radiolabeled BBN(8-14) analogues that were studied to determine their internalization andintracellular trapping efficiencies were radioiodinated (i.e., ¹²⁵I)derivatives. The results of these studies demonstrated that despiterapid interalization after ¹²⁵I-labeled BBN analogue binding to GRPreceptors in Swiss 3T3n cells, the ¹²⁵I was rapidly expelled from thecells [Hoffman et al., 1997] as shown in FIG. 11. Thus, these ¹²⁵I-BBNderivatives were not suitable for further development.

In contrast, the ¹⁰⁵Rh-BBN(8-14) derivatives that bind to GRP receptorsare not only rapidly internalized, but there is a large percentage ofthe ¹⁰⁵Rh activity that remains trapped within the cells for hours (andin some cell lines>twenty four hours). This observation indicates thatthese radiometallated BBN derivatives have real utility asradiopharmaceuticals for in vivo targeting of neoplasms expressing GRPreceptors.

Experiments designed to determine the fraction of a radiotracerinternalized within cells were performed by adding excess ¹²⁵I- or¹⁰⁵Rh-BBN derivatives to the cell incubation medium. After establishmentof equilibrium after a forty minute incubation, the media surroundingthe cells was removed and the cells were washed with fresh mediacontaining no radioactivity. After washing, the quantity ofradioactivity associated with the cells was determined (i.e., totalcounts per min (TCPM) of ¹²⁵I or ¹⁰⁵Rh associated with the cells). Thecells were then incubated in a 0.2M acetic acid solution (pH 2.5) whichcaused the surface proteins (incl., GRP receptors) to denature andrelease all surface bound radioactive materials. After removing thisbuffer and washing, the cells were counted again. The counts per minute(c.p.m.) associated with the cells at that point were only related tothe ¹²⁵I or ¹⁰⁵Rh that remained trapped inside of the cells.

To determine intracellular retention, a similar method was employed.However, after washing the cells with fresh (non-radioactive) incubationmedia, the cells were incubated in the fresh media at different timeperiods after washing away all extracellular ¹²⁵I- or ¹⁰⁵Rh-BBNanalogues. After each time period, the methods used to determine TOTALc.p.m. and intracellular c.p.m. after washing with a 0.2M acetic acidsolution at pH 2.5 were the same as described above and the percent ¹²⁵Ior ¹⁰⁵Rh remaining trapped inside of the cells was calculated. FIG. 12is a graph of results of efflux experiments using. Swiss 3T3 cells with¹²⁵I-Lys³-BBN. The results show that there is rapid efflux of the ¹²⁵Ifrom inside of these cells with less than 50% retained at fifteenminutes and by sixty minutes, less than 20% remained as shown in FIG.12.

In contrast, studies with all of the ¹⁰⁵Rh-[16]aneS₄-BBN agonistderivatives that are internalized inside of the cells showed substantialintracellular retention of ¹⁰⁵Rh by the GRP receptor expressing cells.For example, results of studies using ¹⁰⁵Rh-BBN-37 (see FIG. 9) inconjunction with Swiss 3T3 cells showed that approximately 50% of the¹⁰⁵Rh activity remains associated with the cells at sixty minutespost-washing and approximately 30% of ¹⁰⁵Rh remained inside of the cellsafter four hours as shown in FIG. 13. Note that at least 5% of the ¹⁰⁵Rhis surface bound at ≧sixty minutes.

The ¹⁰⁵Rh-BBN derivatives shown in FIG. 9 all have an amidatedmethionine at position BBN-14 and are expected to be agonists [Jensen etal., 1993]. Therefore, they would be predicted to rapidly internalizeafter binding to GRP receptors on the cell surface [Reile et al., 1994;Bjisterbosch et al., 1995; Smythe et al., 1991], which was confirmed byapplicants' data. Referring to FIG. 14, ¹⁰⁵Rh-BBN-61, a BBN analoguewith no amino acid at position BBN-14 (i.e., a ¹⁰⁵Rh-BBN(8-13)derivative), was synthesized and studied. This BBN analogue has a highbonding affinity (i.e., IC₅₀=30 nM). This type of derivative is expectedto be an antagonist and as such will not internalize [Jensen et al.,1993; Smythe et al., 1991]. Results of efflux studies with ¹⁰⁵Rh-BBN-61using Swiss 3T3 cells showed that immediately following washing withfresh incubation buffer (i.e., t=0), essentially all of the ¹⁰⁵Rhassociated with these cells is on the cell surface, as expected.Furthermore, after only one hour of incubation, less than 10% remainedassociated with these cells in any fashion (see FIGS. 15 and 16). Thesedata indicate that ¹⁰⁵Rh-antagonists with structures similar to the¹⁰⁵Rh-BBN agonists (i.e., those shown in FIG. 9) are not good candidatesfor development of radiopharmaceuticals since they are neither trappedin nor on the GRP receptor expressing cells to nearly the same extent asthe radiometallated BBN agonists.

EXAMPLE III Human Cancer Cell Line Studies

In vitro cell binding studies of ¹⁰⁵Rh-BBN-37 with two different humancancer cell lines that express GRP receptors (i.e., the PC-3 and CF-PAC1cell lines), which are tumor cells derived from patients with prostateCA and pancreatic CA, as shown in FIGS. 17A-B and 18A-B, respectively)were performed. Results of these studies demonstrated consistency with¹⁰⁵Rh-BBN-37 binding and retention studies using Swiss 3T3 cells.Specifically, the binding affinity of Rh-BBN-37 was high (i.e., IC₅₀≅7nM) with both human cancer cell lines as shown in Table 1. In addition,in all cells, the majority of the ¹⁰⁵Rh-BBN-37 was internalized andperhaps a major unexpected result was that the retention of the¹⁰⁵Rh-tracer inside of the cells was significantly better than retentionin Swiss 3T3 cells as shown in FIGS. 17 and 18. For example, it isparticularly remarkable that the percentage of ¹⁰⁵R-BBN-37 that remainedassociated with both the CFPAC-1 and PC-3 cell line was >80% at twohours after removing the extracellular activity by washing with freshincubation buffer (see FIGS. 17 and 18).

EXAMPLE IV In Vivo Studies

Biodistribution studies were performed by intravenous (I.V.) injectionof either ¹⁰⁵Rh-BBN-22 or ¹⁰⁵Rh-BBN-37 into normal mice. In thesestudies, unanesthetized CF-1 mice (15-22 g, body wt.) were injected I.V.via the tail vein with between one (1) to five (5) μCi (37-185 KBq) ofthe ¹⁰⁵Rh-labeled agent. Organs, body fluids and tissues were excisedfrom animals sacrificed at 30, 60 and 120 minutes post-injection (PI).The tissues were weighed, washed in saline (when appropriate) andcounted in a NaI well counter. These data were then used to determinethe percent injected dose (% ID) in an organ or fluid and the % ID pergram. The whole blood volume of each animal was estimated to be 6.5percent of the body weight. Results of these studies are summarized inTables 2 and 3.

Results from these studies showed that both the ¹⁰⁵Rh-BBN-22 and¹⁰⁵Rh-BBN-37 were cleared from the bloodstream, predominantly via thekidney into the urine. Specifically, 68.4±6.6% and 62.3±5.8% of the IDwas found in urine at two hours PI of ¹⁰⁵Rh-BBN-22 and ¹⁰⁵Rh-BBN-37,respectively (see Tables 2 and 3). An unexpected finding was that the %ID of ¹⁰⁵Rh that remained deposited in the kidneys of these animals wasonly 2.4±0.6% ID and 4.6±1.3% ID at two hours PI of ¹⁰⁵Rh-BBN-22 and¹⁰⁵Rh-BBN-37 (see Tables 2 and 3). This is much less than would beexpected from previously reported data where radiometallated peptidesand small proteins have exhibited renal retention of the radiometal thatis >10% ID and usually much >10% [Duncan et al., 1997]. The reason forreduced renal retention of ¹⁰⁵Rh-BBN analogues is not known, however,this result demonstrates a substantial improvement over existingradiometallated peptides.

Biodistribution studies also demonstrated another important in vivoproperty of these radiometallated BBN analogues. Both ¹⁰⁵Rh-BBN-22 and¹⁰⁵Rh-BBN-37 are efficiently cleared from organs and tissues that do notexpress GRP receptors (or those that do not have their GRP-receptorsaccessible to circulating blood). The biodistribution studies in micedemonstrated specific uptake of ¹⁰⁵Rh-BBN-22 and ¹⁰⁵Rh-BBN-37 in thepancreas while other non-excretory organs or tissues (i.e., heart,brain, lung, muscle, spleen) exhibited no uptake or retention (Tables 2and 3). Both ¹⁰⁵Rh-BBN-22 and ¹⁰⁵Rh-BBN-37 were removed from the bloodstream by both the liver and kidneys with a large fraction of the ¹⁰⁵Rhremoved by these routes being excreted into the intestines and thebladder, respectively. It is important to note that the % ID/gm in thepancreas of ¹⁰⁵Rh-BBN-22 and ¹⁰⁵Rh-BBN-37 was 3.9±1.3% and 9.9±5.4%,respectively at 2 hr, PI. Thus, the ratios of % ID/gm of ¹⁰⁵Rh-BBN-22 inthe pancreas relative to muscle and blood were 16.2 and 7.6,respectively. The ratios of % ID/gm of ¹⁰⁵Rh-BBN-37 in the pancreasrelative to muscle and blood were 25.4 and 29.1, respectively. Thesedata demonstrated selective in vivo targeting of these radiometallatedBBN analogues to cells expressing GRP receptors [Zhu et al., 1991; Qinet al., 1994] and efficient clearance from non-target tissues. If cancercells that express GRP receptors are present in the body, these resultsindicate radiometallated BBN analogues will be able to target them witha selectivity similar to the pancreatic cells.

A comparison of the pancreatic uptake and retention of ¹⁰⁵Rh-BBN-22 with¹⁰⁵Rh-BBN-37 demonstrated that ¹⁰⁵Rh-BBN-37 deposits in the pancreaswith a 2-fold better efficiency than ¹⁰⁵Rh-BBN-22 (i.e., 3.6±1.2% ID and2.3±1.0% ID) for ¹⁰⁵Rh-BBN-37 at one and two hours PI, respectively, vs.1.2±0.5% ID and 1.0±0.1% ID for ¹⁰⁵Rh-BBN-22 at one and two hours PI).This data is consistent with the >2-fold higher uptake and retention of¹⁰⁵Rh-BBN-37 found in the in vitro studies shown in FIG. 16.

EXAMPLE V Synthesis and In Vitro Binding Measurement of Synthetic BBNConjugate Analogues Employing Amino Acid Chain Spacers

A. Synthesis

Five BBN analogues were synthesized by SPPS in which between 2 to 6amino acid spacer groups were inserted to separate a S₄-macrocyclicchelator from the N-terminal trp⁸ on BBN(8-14) (FIG. 19). Each peptidewas prepared by SPPS using an Applied Biosystems Model 432A peptidesynthesizer. After cleavage of each BBN analogue from the resin usingTrifluoracetic acid (TFA), the peptides were purified by C₁₈reversed-phase IPLC using a Vydac HS54 column and CH₃CN/H₂O containing0.1% TFA as the mobile phase. After collection of the fractioncontaining the desired BBN peptide, the solvent was evaporated. Theidentity of each BBN peptide was confirmed by FAB-mass spectrometry(Department of Chemistry—Washington University, St. Louis, Mo.).

Various amino acid sequences (in some cases containing different R groupmoieties) were conjugated to the N-terminal end of the BBN bindingregion (i.e., to BBN-8 or Trp⁸). BBN analogue numbers 96, 97, 98, 99 and101 were synthesized as examples of LN-terminal modified peptides inwhich the [16]aneS₄ macrocycle BFCA was separated from trp⁸ on BBN(8-14)by various amino acid sequences as shown in FIG. 19.

The [16]aneS₄ macrocyclic ligand was conjugated to selected tethered BBNanalogues. The —OCH₂COOH group on the [16]andS₄ macrocycle derivativewas activated via HOBt/HBTU so that it efficiently formed an amide bondwith the terminal NH2 group on the spacer side arm (followingdeprotection). The corresponding [16]aneS₄ tethered BBN derivatives wereproduced and examples of 5 of these derivatives (i.e., BBN-96, 97, 98,99 and 101) are shown in FIG. 19. As previously described, each[16]aneS₄ BBN derivative was purified by reversed phase HPLC andcharacterized by FAB Mass Spectroscopy.

B. In Vitro Binding Affinities

The binding affinities of the synthetic BBN derivatives were assessedfor GRP receptors on Swiss 3T3 cells, PC-3 cells and CF PAC-1 cells. TheIC₅₀'s of each of derivative was determined relative to (i.e., incompetition with) ¹²⁵I-Tyr⁴-BBN. The cell binding assay methods used tomeasure the IC₅₀'s is standard and was used by techniques previouslyreported [Jensen et al., 1993; Cai et al., 1992; Cal et al., 1994]. Themethods used for determining IC₅₀'s with all BBN analogue binding to GRPrepectors present on all three cell lines was similar. The specificmethod used to measure IC₅₀'s on Swiss 3T3 cells is briefly described asfollows:

Swiss 3T3 mouse fibroblasts are grown to confluence in 48 wellmicroliter plates. An incubation media was prepared consisting of HEPES(11.916 g/l), NaCl (7.598 g/l), KCl (0.574 g/l), MgCl₂ (1.106 g/l), EGTA(0.380 g/l), BSA (5.0 g/l), chymostatin (0.002 g/l), soybean trypsininhibitor (0.200 g/l), and bacitracin (0.050 g/l). The growth media wasremoved, the cells were washed twice with incubation media, andincubation media was returned to the cells. ¹²⁵I-Tyr⁴-BBN (0.01 μCi) wasadded to each well in the presence of increasing concentrations of theappropriate competitive peptide. Typical concentrations of displacingpeptide ranged from 10⁻¹² to 10⁻⁵ moles of displacing ligand per well.The cells were incubated at 37° C. for forty minutes in a 95% O₂/5% CO₂humidified environment. At forty minutes post initiation of theincubation, the medium was discarded, and the cells were washed twicewith cold incubation media. The cells were harvested from the wellsfollowing incubation in a trypsin/EDTA solution for five minutes at 37°C. Subsequently, the radioactivity, per well, was determined and themaximum % total uptake of the radiolabeled peptide was determined andnormalized to 100%. A similar procedure was used in performing cellbinding assays with both the PC-3 and CF_(a)-PAC-1 human cancer celllines.

C. Results of Binding Affinity Measurements

The IC₅₀ values measured for the BBN derivatives synthesized inaccordance with this invention showed that appending a chelator viaamino acid chain spacer groups via the N-terminal BBN-8 residue (i.e.,Trp⁸) produced a variation of IC₅₀ values. For example, see IC₅₀ valuesshown for BBN 96, 97, 98 and 101 in FIG. 19. The observations areconsistent with previous reports showing variable IC₅₀ values whenderivatizing BBH(8-13) with a predominantly short chain of amino acidresidues [Hoffken, 1994]. When the amino acid spacer groups used inBBN-98, 99 and 101 were appended between BBN(7-14) and the [16]aneS₄macrocyle, the IC₅₀'s were found to be surprisingly constant and in the1-6 nM range for all three cell lines (i.e., see IC₅₀ values shown inFIG. 19). These data suggest that using relatively simple spacer groupscomposed entirely of selected amino acid sequences to extend ligandssome distance from the BBN region [e.g., BBN(8-14) can producederivatives that maintain binding affinities in the 1-6 nmolar range.

D. Cell Binding Studies with Rh-BBN-Conjugates

Results illustrated in FIG. 20 show that when the corresponding RhCl₂[16]aneS₄ complex was separated from Trp⁸ on BBH(8-14) by the fourdifferent amino acid spacer groups (see FIG. 20), the IC₅₀'s of all fouranalogues (i.e., BBN-97, -98, -99, -101) were between 0.73 and 5.29nmolar with GRP receptors on the PC-3 and CF PAC-1 cell lines. TheIC₅₀'s for these same Rh-BBN conjugates were somewhat higher with theSwiss 3T3 cell line (FIG. 20). These data demonstrate that amino acidchain with spacer groups used to move the +1 charged Rh-S₄-chelate awayfrom the BBN binding region will result in a metallated BBN analoguewith sufficiently high binding affinities to GRP receptors for in vivotumor targeting applications.

EXAMPLE VI Synthesis and In Vitro Binding Assessment of a^(99m)-Tc-Labeled Synthetic BBN Analogue

A. Synthesis

Several tetradentate chelating frameworks have been used to form stable^(99m)Tc or ¹⁸⁸Re labeled peptide and protein conjugates [Eckelman,1995; Li et al., 1996b; Parker, 1990; Lister-James et al., 1997]. Manyof these ligand systems contain at least one thiol (—SH) donor group tomaximize rates of formation and stability (both in vitro and in vivo) ofthe resultant Tc(V) or Re(V) complexes [Parker, 1990; Eckelman, 1995].Results from a recent report indicates that the bifunctional chelatingagent (BFCA) (dimethylglycyl-L-seryl-L-cyteinyl-glycinamide (N₃S-BFCA)is capable of forming a well-defined complex with ReO⁺³ and TcO⁺³ [Wonget al., 1997]. Since this ligand framework can be synthesized by SPPStechniques, this N₃S-BFCA was selected for use in forming ofTc-99m-BBN-analogue conjugates. Three different N₃S-BFCA conjugates ofBBN(7-14) were synthesized (BBN-120, -121 and -122) as shown in FIG. 21by SPPS. BBN-120, BBN-121 and BBN-122 represent a series of analogueswhere the N₃S-BFCA is separated from the BBN(7-14) sequence by a 3, 5and 8 carbon spacer groups (FIG. 21). Each peptide was synthesized andpurified using the SPPS and chromatographic procedures outlined inExample 1. The thiol group on cystein was protected using the ACM group,which is not cleaved during cleavage of these BBN-conjugates from theresin using TFA. The identity of BBN-120, -121 and -122 was confirmed byFAB mass spectrometry. Synthesis and purification of the N₃S-BFCA couldalso be readily accomplished using SPPS methods, followed by HPLCpurification (see Example 1). The ACM group was used to protect thethiol group on cysteine during synthesis and cleavage from the resin.

B. In Vitro Binding Affinities

Synthesis of ^(99m)Tc-BBN-122 (FIG. 22) was prepared by two methods[i.e., (1) by transchelation of ^(99m)TcO⁺³ from ^(99m)Tc-gluconate or(2) by formation of the “preformed” ^(99m)Tc-BFCA complex followed by—COOH activation with tetrafluorophenyl and subsequent reaction with theC₅-carbon spacer group appended to BBN(7-14)]. In both cases, the^(99m)Tc-labeled peptide formed is shown in FIG. 22. The structure ofthis Tc-BBN-122 conjugate was determined by using non-radioactive Re(the chemical congener of Tc). In these studies, the “preformed” ReO⁺³complex with the N₃S-BFCA was prepared by reduction of ReO₄; with SnCl₂in the presence of excess N₃S-BFCA dissolved in sodium phosphatebuffered water at pH 6-6.5 by a method previously published [Wong etal., 1997]. After purification of the ReO—N₃S-BFCA complex, thestructure of this chelate was shown (by Mass-Spect) to be identical tothat previously reported [Wong et al., 1997].

The ReO—N₃—S-BFCA complex was converted to the activated trifluorophenyl(TFP) ester by adding 10 mg of the complex to 6 mg (dry) EDC and the 50μl of TFP. After the solution was vortexed for one minute, CH₃CN wasadded until disappearance of cloudiness. The solution was incubated forone hour at RT and purified by reversed-phase HPLC. To prepare theReO—N₃S-BFCA complex BBN-122 conjugate (FIG. 22), one μl of the HPLCfraction containing the ReO—N₃S-BFCA complex was added to a solutioncontaining 1 mg of the C₈-tethered BBN(7-14) peptide in 0.2 N NaHCO₃ atpH 9.0. After incubation of this solution for one hour at RT, the samplewas analyzed and purified by reversed-phase HPLC. The yield ofRe-BBN-122 was approximately 30-35%.

The method for preparation of the corresponding ^(99m)Tc-BBN-122conjugate, using the “preformed” ^(99m)TcO—N₃S-BFCA complex, was thesame as described above with the “preformed” ReO—N₃S-BFCA complex. Inthis case, ^(99m)TcO₄, from a ⁹⁹Mo/^(99m)Tc generator, was reduced withan aqueous saturated stannous tartrate solution in the presence ofexcess N₃S-BFCA. The yields of the ^(99m)Tc-BBN-122 product using this“preformed” method were approximately 30-40%. Reversed phase HPLCanalysis of the 99mTc-BBN-122, using the same gradient elution program¹as used for analysis of the Re-BBN-122 conjugate, showed that both the^(99m)Tc-BBN-122 and ¹⁸⁸Re-BBN-122 had the same retention time (i.e.,14.2-14.4 min) (See FIG. 22). This provides strong evidence that thestructure of both the ^(99m)Tc-BBN-122 and Re-BBN-122 are identical.¹ Gradient elution program used in these studies was as follows. Flow1.5 ml/minute Solvent A=HO with 0.1% TFA Solvent B=CHCN with 0.1% TFA

The binding affinities of BBN-122 and Re-BBN-122 were assessed for GRPreceptors on Swiss 3T3 cells, PC-3 cells and CFPAC-1 cells that expressGRP receptors. The IC₅₀'s of each derivative was determined relative to(i.e., in competition with) ¹²⁵I-Tyr⁴-BBN (the K_(d) for ¹²⁵I-Tyr⁴-BBNfor GRP receptors in Swiss 3T3 cells is reported to be 1.6±0.4 nM) [Zhuet al., 1991]. The cell binding assay methods used to measure the IC₅₀'sis standard and was used by techniques previously reported [Leban etal., 1994; Cai et al., 1994; Cai et al., 1992]. The methods used fordetermining IC₅₀'s with all GRP receptor binding of GRP receptors on allcell lines was similar and has been described previously for the otherBBN-analogues and Rh-BBN analogues described in this document.

C. Results of Binding Affinity Measurements

The IC₅₀ values measured for BBN-122 and Re-BBN-122 synthesized inaccordance with this invention showed that appending an Time (minutes) %A/% B 0 95/5 25  30/70 35 95/5

8-carbon hydrocarbon chain spacer linked to the N₂S₁-BFCA and thecorresponding Re complex (i.e., Trp⁸) produced BBN conjugates with IC₅₀values in a 1-5 nmolar range (See Table A). When ^(99m)Tc-BBN-122 wasincubated with these same cells, it was shown that ≧nmolarconcentrations of BBN displaced this ^(99m)Tc conjugate by >90%. Thisresult demonstrates that ^(99m)Tc-BBN-122 has high and specific bindingaffinity for GRP receptors. These data suggest that using relativelysimple spacer groups to extend the N₃S ligand framework and thecorresponding Tc-or Re-N₃S₁, complexes some distance from the BBNbinding region can produce derivatives that maintain binding affinitiesin the 1-5 nmolar range. TABLE A Summary of IC₅₀ values for GRP receptorbinding for the non-metallated BBN-122 conjugate or the Re-BBN-122conjugate in two cell lines (PC-3 and CF-PAC-1 cell lines that expressGRP receptors). The IC₅₀ values were measured using cell binding assaysrelative to ¹²⁵I-Tyr⁴-BBN. IC₅₀ (nmolar) Conjugate PC-3 CF-PAC1 BBN-1223.59 ± 0.75 (n = 6) 5.58 ± 1.92 (n = 14) Re-BBN-122 1.23 ± 0.56 (n = 12)1.47 ± 0.11 (n = 6)

EXAMPLE VII Retention of 99mTc-BBN-122 in Human Cancer Cells PC-3 andCF-PAC-1 Cells)

Once the radiometal has been specifically “delivered” to cancer cells(e.g., employing the BBN binding moiety that specifically targets GRPreceptors on the cell surface), it is necessary that a large percentageof the “delivered” radioactive atoms remain associated with the cellsfor a period time of hours or longer to make an effectiveradiopharmaceutical for effectively treating cancer. One way to achievethis association is to internalize the radiolabeled BBN conjugateswithin the cancer cell after binding to cell surface GRP receptors.,

Experiments designed to determine the fraction ^(99m)Tc-BBN-122internalized within cells were performed by the same method previouslydescribed for ¹⁰⁵Rh-BBN-37. Briefly, excess ^(99m)Tc-BBN-122 was addedto PC-3 or CFPAC-1 cell incubation media and allowed to establishequilibrium after a forty minute incubation. The media surrounding thecells was removed and the cells were washed with fresh media containingno radioactivity. After washing, the quantity of radioactivityassociated with the cells was determined (i.e., total counts per min^(99m)Tc associated with cells). The PC-3 and CFPAC-1 cells were thenincubated in a 0.2M acetic acid solution (pH2.5) which caused thesurface proteins (including GRP receptors) to denature and release allsurface bound radioactive materials. After removing this buffer andwashing, the cells were counted again. The counts per minute (c.p.m.)associated with the cells at that point were only related to the^(99m)Tc that remained trapped inside of the PC-3 or CFPAC-1 cells.

To determine intracellular retention of ^(99m)Tc activity, a similarmethod was employed. However, after washing the cells with fresh(non-radioactive) incubation media, the cells were incubated in thefresh media at different time period after washing away allextracellular ^(99m)Tc-BBN-122. After each time interval, the methodsused to determine total c.p.m. and intracellular c.p.m. by washing witha 0.2M acetic acid solution at pH 2.5.

Studies with the ^(99m)Tc-BBN-122 agonist show that it is internalizedinside of the PC-3 and CFPAC-1 cells (FIGS. 23-26) and that substantialintracellular retention of ^(99m)Tc by the GRP receptor expressing cellsoccurs. For example, results of studies using ^(99m)Tc-BBN-122 inconjunction with PC-3 cells showed a high rate of internalization (FIG.23) and that approximately 75% of the ^(99m)Tc activity remainsassociated with the cells at ninety minutes post-washing (FIG. 25).Almost all of this ^(99m)Tc cell-associated activity is inside of thePC-3 cells. Similar results were also found with the CFPAC 1 cells wherethere is also a high rate of ^(99m)Tc-BBN-122 internalization (FIG. 24)and relatively slow efflux of ^(99m)Tc from the cells (i.e., 50-60%retention at 120 min post-washing (FIG. 26).

The ^(99m)Tc-BBN-122 peptide conjugate shown in FIG. 22 has an amidatedmethionine at position BBN-14 and is expected to be an agonists [ensenet al., 1993]. Therefore, it would be predicted to rapidly internalizeafter binding to GRP receptors on the cell surface (Bjisterbosch et al.,1995; Smythe et al., 1991], which is confirmed by applicants' data inFIG. 23-26.

EXAMPLE VIII In Vivo Studies

Biodistribution studies were performed by intravenous (I.V.) injectionof ^(99m)Tc-BBN-122 into normal mice. In these studies, unanesthetizedCF-1 mice (15-22 g, body wt.) were injected I.V. via the tail vein withbetween one (1) to five (5) μCi (37-185 KBq) of ^(99m)Tc-BBN-122.Organs, body fluids and tissues were excised from animals sacrificed at0.5, 1, 4 and 24 hours post-injection (PI). The tissues were weighed,washed in saline (when appropriate) and counted in a NaI well counter.These data were then used to determine the percent injected dose (% ID)in an organ or fluid and the % ID) per gram. The whole blood volume ofeach animal was estimated to be 6.5 percent of the body weight. Resultsof these studies are summarized in Tables B and C.

Results from these studies showed that ^(99m)Tc-BBN-122 is cleared fromthe blood stream predominantly via the hepatobiliary pathway shavingabout 35% of the ^(99m)Tc-activity cleared via the kidney into theurine. Specifically, 33.79±1.76% of the ID was found in urine at onehour PI (Table B). The retention of ^(99m)Tc activity in the kidneys andliver is very low (Table B). This is much less than would be expectedfrom previously reported data where radiometallated peptides and smallproteins have exhibited renal retention of the radiometal that is >10%ID and usually much >10% [Duncan et al., 1997]. The reason for reducedrenal retention of ^(99m)Tc-BBN-122 is not known, however, this resultdemonstrates a substantial improvement over existing radiometallatedpeptides.

Biodistribution studies also demonstrated another important in vivoproperty of ^(99m)Tc-BBN-122 in that it is efficiently cleared fromorgans and tissues that do not express GRP receptors (or those that donot have their GRP-receptors accessible to circulating blood). Thebiodistribution studies in mice demonstrated specific uptake of^(99m)Tc-BBN-122 in the pancreas while other non-excretory organs ortissues (i.e., heart, brain, lung, muscle, spleen) exhibited no uptakeor retention. ^(99m)Tc-BBN-122 is removed from the blood stream by boththe liver and kidneys with a large fraction of the ^(99m)Tc removed bythese routes being excreted into the intestines and the bladder,respectively. It is important to note that the % ID/gm in the pancreasof ^(99m)Tc-BBN-122 is 12.63%/gm at 1 hour and drops to only 5.05% atthe 4 hour PI (Table C). Thus, the ratios of % ID/gm of ^(99m)Tc-BBN-122in the pancreas relative to muscle and blood were 92.2 and 14.78 at 4hour PI, respectively. These data demonstrated selective in vivotargeting of this ^(99m)Tc-labeled BBN analogue to cells expressing GRPreceptors [Zhu et al., 1991; Qin et al., 1994] and efficient clearancefrom non-target tissues. If cancer cells that express GRP receptors arepresent in the body, these results indicate 99mTc-BBN analogues will beable to target them with a selectivity similar to the pancreatic cells.TABLE B Biodistribution of ^(99m)Tc-BBN-122 in normal CF-1 mice at 0.5,1, 4 and 24 hr post-IV injection. Results expressed as % ID/organ %Injected Dose/Organ^(a) Organ^(c) 30 min 1 hr 4 hr 24 hr Blood^(d) 3.52± 2.16 1.08 ± 0.34 0.59 ± 0.24 0.12 ± 0.01 Liver 4.53 ± 0.93 4.77 ± 1.401.49 ± 0.32 0.32 ± 0.06 Stomach 2.31 ± 0.45 1.61 ± 0.81 1.75 ± 0.20 0.30± 0.06 Lg. Intestine^(b) 2.84 ± 0.32 24.17 ± 7.91  23.85 ± 7.02  0.61 ±0.14 Sm. Intestine^(b) 43.87 ± 1.51  23.91 ± 9.08  5.87 ± 7.09 0.42 ±0.06 Kidneys^(b) 1.49 ± 0.19 1.15 ± 0.10 0.55 ± 0.06 0.20 ± 0.01Urine^(b) 26.78 ± 1.05  33.79 ± 1.76  ˜35 ˜35 Muscle 0.02 ± 0.01 0.01 ±0.00 0.01 ± 0.01 0.01 ± 0.01 Pancreas 5.30 ± 0.63 3.20 ± 0.83 1.21 ±0.13 0.42 ± 0.17^(a)Each value in the table represents the mean and SD from 5 animals ineach group.^(b)At 4 and 24 hr, feces containing ^(99m)Tc had been excreted fromeach animal and the % ID in the urine was estimated to be approximately60% of the ID.^(c)All other organs excised (incl. brain, heart, lung and spleen)showed <0.10% at t ≧1 hr.^(d)% ID in the blood estimated assuming the whole blood volume is 6:5%of the body weight.

TABLE C Biodistribution of ^(99m)Tc-BBN-122 in normal CF-1 mice at 0.5,1, 4 and 24 hr post I.V. injection. Results expressed as % ID/gm. %Injected Dose/gm^(a) Organ 30 min 1 hr 4 hr 24 hr Blood^(b) 2.00 ± 1.280.63 ± 0.19 0.34 ± 0.11 0.08 ± 0.00 Liver 2.70 ± 0.41 3.14 ± 0.81 0.96 ±0.20 0.22 ± 0.05 Kidneys 3.99 ± 0.76 3.10 ± 0.31 1.58 ± 0.15 0.64 ± 0.08Muscle 0.23 ± 0.08 0.13 ± 0.02 0.05 ± 0.01 0.01 ± 0.01 Pancreas 16.89 ±0.95  12.63 ± 1.87  5.05 ± 0.42 1.79 ± 0.71 P/Bl and P/M Uptake RatiosPancreas/ 8.42 19.76 14.78 20.99 Blood ancreas/ 73.16 93.42 92.25 142.76Muscle^(a)Each value in the table represents the mean and SD from 5 animals ineach group.^(b)% ID in the blood estimated assuming the whole blood volume is 6:5%of the body weight.

TABLE D Biodistribution of ^(99m)Tc-BBN-122 in PC-3 tumor bearing SCIDmice at 1, 4 and 24 hr post-I.V. injection. Results expressed as %ID/organ. Tumor Line: PC-3 % ID per Organ^(a) Organ^(c) 1 hr 4 hr 24 hrBlood^(b) 1.16 ± 0.27 0.47 ± 0.06 0.26 ± 0.05 Liver 1.74 ± 0.64 0.72 ±0.10 0.29 ± 0.05 Stomach 0.43 ± 0.18 0.29 ± 0.22 0.08 ± 0.02 Lg.Intestine  9.18 ± 19.42 42.55 ± 8.74  0.64 ± 0.17 Sm. Intestine 46.55 ±16.16 2.13 ± 0.76 0.31 ± 0.04 Kidneys 1.16 ± 0.20 0.60 ± 0.06 0.16 ±0.01 Urine^(d) 32.05 ± 12.78 ˜35 ˜35 Muscle 0.01 ± 0.00 0.00 ± 0.00 0.00± 0.00 Pancreas 1.69 ± 0.61 1.05 ± 0.13 0.34 ± 0.08 Tumor 1.00 ± 0.780.49 ± 0.08 0.49 ± 0.25^(a)Each value in the table represents the mean and SD from 5 animals ineach group.^(b)At 4 and 24 hr, feces containing ^(99m)Tc had been excreted fromeach animal and the % ID in the urine was estimated to be approximately60% of the ID.^(c)All other organs excised (incl. brain, heart, lung and spleen)showed <0.10% at t ≧1 hr.^(d)% ID in the blood estimated assuming the whole blood volume is 6:5%of the body weight.

TABLE E Biodistribution of ^(99m)Tc-BBN-122 in PC-3 tumor bearing SCIDmice at 1, 4 and 24 hr post-I.V. injection. Results expressed as %ID/Gm. Tumor Line: PC-3 % ID per gm^(a) Organ 1 hr 4 hr 24 hr Blood^(b)0.97 ± 0.26 0.31 ± 0.03 0.18 ± 0.04 Liver 2.07 ± 0.88 0.64 ± 0.05 0.26 ±0.04 Kidneys 4.80 ± 1.33 2.23 ± 0.35 0.60 ± 0.04 Muscle 0.18 ± 0.12 0.06± 0.03 0.05 ± 0.04 Pancreas 10.34 ± 3.38  5.08 ± 1.12 1.47 ± 0.23 Tumor2.07 ± 0.50 1.75 ± 0.61 1.28 ± 0.22 T/Bl, T/M, P/Bl and P/M UptakeRatios Tumor/Blood 2.13 5.52 6.79 Tumor/Muscle 11.44 25.38 21.62Pancreas/Blood 10.64 15.96 7.81 Pancreas/Muscle 57.14 73.40 24.87^(a)Each value in the table represents the mean and SD from 5 animals ineach group.^(b)% ID in the blood estimated assuming the whole blood volume is 6:5%of the body weight.

The invention has been described in an illustrative manner, and it is tobe understood that the terminology which has been used is intended to bein the nature of words of description rather than of limitation.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is, therefore, to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically describe.

Throughout this application, various publications are referenced bycitation and number. Full citations for the publication are listed belowthe disclosure of these publications in their entireties are herebyincorporated by reference into this application in order to more fullydescribe the state of the art to which this invention pertains.

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TABLE 2 Complex ¹⁰⁵Rh-Peptide22 ¹⁰⁵Rh-Peptide22 ¹⁰⁵Rh-Peptide22 30 min 1hr 2 hr n = 9 n = 9 n = 9 (% Dose) Organ (% Dose) Brain 0.08 ± 0.02 0.04± 0.01 0.06 ± 0.09 Blood 4.48 ± 1.24 1.86 ± 0.38 0.99 ± 0.24 Heart 0.13± 0.03 0.08 ± 0.03 0.04 ± 0.04 Lung 0.25 ± 0.08 0.20 ± 0.09 0.15 ± 0.09Liver 7.97 ± 2.85 8.51 ± 2.33 8.57 ± 2.04 Spleen 0.07 ± 0.03 0.09 ± 0.080.05 ± 0.01 Stomach 1.11 ± 0.76 0.59 ± 0.21 0.30 ± 0.16 Large Intestine0.73 ± 0.16 3.21 ± 3.38 8.91 ± 3.79 Small Intestine 6.29 ± 1.87 6.98 ±1.87 3.48 ± 1.78 Kidneys 4.25 ± 1.33 3.25 ± 0.60 2.44 ± 0.64 Bladder44.66 ± 7.29  62.88 ± 3.84  68.41 ± 6.63  Muscle 0.06 ± 0.03 0.03 ± 0.030.01 ± 0.01 Pancreas 0.95 ± 0.46 1.15 ± 0.49 1.01 ± 0.14 Carcass 32.90 ±6.61  12.62 ± 4.77  6.37 ± 1.17 (% Dose/GM) Organ (% D/GM) Brain 0.21 ±0.07 0.14 ± 0.08 0.16 ± 0.28 Blood 2.22 ± 0.40 1.02 ± 0.22 0.51 ± 0.11Heart 0.92 ± 0.25 0.64 ± 0.20 0.38 ± 0.33 Lung 1.44 ± 0.33 1.24 ± 0.540.92 ± 0.69 Liver 4.33 ± 1.52 5.18 ± 1.52 5.17 ± 1.12 Spleen 0.86 ± 0.381.10 ± 0.65 0.84 ± 0.53 Stomach 2.46 ± 1.65 1.53 ± 0.74 0.71 ± 0.33Large Intestine 0.78 ± 0.19 4.42 ± 4.62 10.10 ± 4.58  Small Intestine4.73 ± 1.47 5.84 ± 1.81 2.86 ± 1.47 Kidneys 7.57 ± 1.49 6.70 ± 0.75 4.60± 0.83 Muscle 0.53 ± 0.32 0.61 ± 0.97 0.24 ± 0.24 Pancreas 3.12 ± 0.994.31 ± 1.98 3.88 ± 1.25

TABLE 3 Complex ¹⁰⁵Rh-Pept37 ¹⁰⁵Rh-Pept37 ¹⁰⁵Rh-Pept37 30 min 1 hr 2 hrn = 5 n = 9 n = 7 (% Dose) Organ (% Dose) Brain 0.03 ± 0.01 0.07 ± 0.110.03 ± 0.03 Blood 3.09 ± 0.54 1.46 ± 0.62 0.66 ± 0.26 Heart 0.12 ± 0.030.05 ± 0.03 0.04 ± 0.02 Lung 0.26 ± 0.09 0.12 ± 0.07 0.08 ± 0.11 Liver13.04 ± 1.93  13.00 ± 3.59  10.12 ± 1.86  Spleen 0.21 ± 0.13 0.16 ± 0.080.10 ± 0.04 Stomach 0.80 ± 0.34 0.65 ± 0.52 0.83 ± 0.96 Large Intestine2.05 ± 0.69 2.96 ± 1.67 8.07 ± 2.25 Small Intestine 8.44 ± 1.89 11.38 ±3.02 5.04 ± 2.27 Kidneys 7.82 ± 2.52 6.04 ± 1.68 4.57 ± 1.29 Bladder39.65 ± 7.21  51.82 ± 7.53  62.32 ± 5.78  Muscle 0.06 ± 0.03 0.02 ± 0.010.02 ± 0.02 Pancreas 2.73 ± 1.14 3.63 ± 1.22 2.25 ± 1.02 Carcass 24.35 ±7.69  9.81 ± 2.91 6.37 ± 1.73 (% Dose/Gm) Organ (% D/GM) Brain 0.10 ±0.05 0.26 ± 0.41 0.10 ± 0.09 Blood 1.60 ± 0.30 0.72 ± 0.31 0.34 ± 0.15Heart 0.92 ± 0.26 0.38 ± 0.21 0.28 ± 0.17 Lung 1.52 ± 0.48 0.76 ± 0.470.46 ± 0.50 Liver 7.31 ± 1.15 7.65 ± 1.29 6.30 ± 1.73 Spleen 2.18 ± 1.171.59 ± 0.71 1.05 ± 0.44 Stomach 1.53 ± 0.67 1.63 ± 1.17 2.18 ± 2.35Large Intestine 2.46 ± 0.70 3.80 ± 2.42 11.84 ± 4.39  Small Intestine5.69 ± 1.26 7.85 ± 1.87 3.81 ± 2.01 Kidneys 14.28 ± 2.84  11.21 ± 3.68 8.39 ± 2.36 Muscle 0.73 ± 0.39 0.20 ± 0.14 0.39 ± 0.38 Pancreas 14.02 ±3.23  15.54 ± 6.21  9.91 ± 5.35

1-85. (canceled)
 86. A compound having a structure of the formulaX-(Y)_(n)-B, wherein X is a metal binding moiety optionally bound to ametal, Y is a spacer group, n is selected from the integers 0 and 1, andB is a bombesin agonist.
 87. The compound of claim 86, wherein Y isselected from the group consisting of an amino acid sequence, ahydrocarbon chain, and a combination thereof.
 88. The compound of claim87, wherein Y is a combination of L-glutamine and a hydrocarbon chain.89. The compound of claim 88, wherein Y is a combination of L-glutamineand a C₁ to C₁₀ hydrocarbon chain.
 90. The compound of claim 86, whereinX is selected from the group consisting of S₄, N₃S, N₂S₂, and NS₃. 91.The compound of claim 90, wherein X is N₃S.
 92. The compound of claim86, wherein said bombesin agonist is BBN(8-14).
 93. The compound ofclaim 86, wherein said bombesin agonist is BBN(8-13).
 94. A complexcomprising a metal and a compound having a structure of the formulaX-(Y)_(n)-B, wherein X is a metal binding moiety, Y is a spacer group, nis selected from the integers 0 and 1, B is a bombesin agonist, and themetal is a diagnostically or therapeutically useful metal.
 95. Thecomplex of claim 94 wherein said metal is a β- or γ-emitting isotope.96. The complex of claim 95, wherein said metal is selected from thegroup consisting of ¹⁸⁶Re—, ¹⁸⁸Re—, ¹⁰⁵Rh—, and ^(99m)Tc—.
 97. Thecomplex of claim 94, wherein Y is selected from the group consisting ofan amino acid sequence, a hydrocarbon chain, and a combination thereof.98. The complex of claim 97, wherein Y is a combination of L-glutamineand a hydrocarbon chain.
 99. The complex of claim 98, wherein Y is acombination of L-glutamine and a C₁ to C₁₀ hydrocarbon chain.
 100. Thecomplex of claim 94, wherein X is selected from the group consisting ofS₄, N₃S, N₂S₂, and NS₃.
 101. The complex of claim 100, wherein X is N₃S.102. The complex of claim 94, wherein said bombesin agonist isBBN(8-14).
 103. The complex of claim 94, wherein said bombesin agonistis BBN(8-13).
 104. A method of imaging a tumor site in a patientcomprising administering to a subject a diagnostically effective amountof a compound comprising a metal complexed with a chelating groupattached to a bombesin agonist and said compound has a structure of theformula X-(Y)_(n)-B, wherein X is a metal binding moiety, Y is a spacergroup, n is selected from the integers 0 and 1, and B is a bombesinagonist.
 105. The method of claim 104, wherein said metal is a β- orγ-emitting isotope.
 106. The method of claim 105, wherein said metal isselected from the group consisting of ¹⁸⁶Re—, ¹⁸⁸Re—, ¹⁰⁵Rh—, and^(99m)Tc—.
 107. The method of claim 104, wherein Y is selected from thegroup consisting of an amino acid sequence, a hydrocarbon chain, and acombination thereof.
 108. The method of claim 107, wherein Y is acombination of L-glutamine and a hydrocarbon chain.
 109. The method ofclaim 108, wherein Y is a combination of L-glutamine and a C₁ to C₁₀hydrocarbon chain.
 110. The method of claim 104, wherein X is selectedfrom the group consisting of S₄, N₃S, N₂S₂, and NS₃.
 111. The method ofclaim 110, wherein X is N₃S.
 112. The method of claim 104, wherein saidbombesin agonist is BBN(8-14).
 113. The method of claim 104, whereinsaid bombesin agonist is BBN(8-13).